Field of the Invention
The present invention relates to an evaporated-fuel processing apparatus for processing evaporated fuel.
Description of the Related Art
For example, in vehicles having an internal combustion engine, when a fuel tank is refilled, the volume occupied by liquid fuel in the internal space of the fuel tank increases. Therefore, the volume of the vapor-phase region in the internal space decreases, so that the pressure of the vapor-phase region (which may be referred to as the tank internal pressure) becomes higher than the atmospheric pressure. Then, the evaporated fuel in the vapor phase staying in the fuel tank tends to be emitted to the atmosphere. If the evaporated fuel is emitted to the atmosphere, the atmosphere is polluted.
In order to prevent the air pollution caused by the emission of the evaporated fuel, in a conventional evaporated-fuel processing apparatus, a canister having absorbent which temporarily absorbs the evaporated fuel is arranged in a communication path between the fuel tank and the atmosphere, so that the evaporated fuel in the vapor phase overflown from the fuel tank is absorbed by the absorbent in the canister. That is, the conventional evaporated-fuel processing apparatus is configured to suppress the tank internal pressure while suppressing emission of the evaporated fuel to the atmosphere.
For example, Japanese Patent Laid-open No. 2004-156494 (which is hereinafter referred to as JP2004-156494A) discloses an evaporated-fuel processing apparatus in which a sealing valve for controlling the state of communication between the fuel tank and the canister is arranged in a flow path for the evaporated fuel realizing communication between the fuel tank and the canister. According to the evaporated-fuel processing technique disclosed in JP2004-156494A, when the internal combustion engine is stopped, the sealing valve is brought into a closed state, and the canister is opened to the atmosphere. In addition, when the internal combustion engine is stopped and a pressure difference exceeding a valve-opening threshold occurs between the tank internal pressure and the atmospheric pressure, the sealing valve is opened. Then, the change in the tank internal pressure which is caused by the opening of the sealing valve is detected. When the detected change in the tank internal pressure is smaller than a predetermined threshold, it is determined that a clogging failure (a failure in which the closed state continues) occurs in the sealing valve.
According to the evaporated-fuel processing technique disclosed in JP2004-156494A, the clogging failure of the sealing valve for sealing the fuel tank can be efficiently detected.
Further, according to the evaporated-fuel processing technique disclosed in JP2004-156494A, when an operator manipulates a lid switch, which is to be manipulated for unlocking a fuel lid covering a fuel filler port, first, the sealing valve is opened in order to prevent emission of the evaporated fuel through the fuel filler port to the atmosphere. The opening of the sealing valve causes a gradual decrease in the tank internal pressure. When the tank internal pressure is lowered to the vicinity of the atmospheric pressure, the fuel lid is unlocked. Thereafter, when the operator manually closes the fuel lid, the operator's manipulation is detected by an open/closed-state detector, and the sealing valve is closed.
However, according to the evaporated-fuel processing technique disclosed in JP2004-156494A, in the case where a failure in which the output value of a sensor detecting the tank internal pressure is stuck to a vicinity of the atmospheric pressure occurs, even when the tank internal pressure is actually high, the sensor outputs a wrong value indicating the tank internal pressure is in the vicinity of the atmospheric pressure, so that the fuel lid can be erroneously unlocked. As a result, it is impossible to perform refueling so as to prevent air pollution.
In view of above, the object of the present invention is to provide an evaporated-fuel processing apparatus which enables refueling so as to prevent air pollution.